1. Field of Invention
The present invention relates to a method of separating a mixture, which method comprises the steps of: mixing a fluid into the mixture; conducting the mixture comprising the fluid via an inlet duct into a separator; allowing the mixture comprising said fluid to separate in the separator into a water phase and an oil/fluid phase; removing the water phase from said separator via an outlet for water and the oil/fluid phase via at least one outlet for oil/fluid; and subjecting the oil/fluid phase to a separation step, separating the oil/fluid phase into an oil phase and a gaseous phase, from which gaseous phase the fluid is recovered by a condensation step and recycled for injection into the mixture.
2. Description of the Prior Art
A method of this kind is disclosed in GB 1 364 942 directed at deoiling and dewatering refinery sludges by use of light hydrocarbons. These sludges occur at oil refineries and comprise sediments in tanks, waste chemicals, emulsions, catalyst rust generated over years and water and oil. The refinery sludges are contacted with light hydrocarbons to obtain phase separation of oil from solids and water-solids phase. The separator acts on phases that are either solid or liquid, and the fluid added to the mixture is maintained in liquid state until the final separation step where the fluid is heated to a temperature in the range of 135-199° C. and allowed to separate from the oil in a fractionating tower. This method is requires a considerable amount of energy and is not suitable for mixtures having a high content of water.
EP 0 963 228 B1 discloses a process for extraction of dispersed and dissolved hydrocarbon contaminants from water. A fluid is injected into the water contaminated with hydrocarbons before the water is treated in a hydrocyclone. The fluid is a condensate from natural gas and is kept in liquid form during the process, so that the hydrocarbon and the fluid can form a single liquid phase. Consequently, the process has to be performed at high pressures of at least 30 bar or more. Compared with earlier processes the process disclosed in EP 0 963 228 B1 is capable of treating a large amount of contaminated water and is capable of cleaning the water to be discharged to have content of impurities not exceeding 40 ppm. And WO 98/37941 describes a process for simultaneously extraction of dispersed and dissolved hydrocarbon contaminants from water.